Light source device

ABSTRACT

A light source device includes: a plurality of laser light sources, each configured to emit a light beam; a plurality of collimating lenses, each configured to collimate the light beam emitted from a corresponding one of the laser light sources; a first transmission diffraction grating configured to diffract and combine, in an identical diffraction angle direction, the light beams transmitted through the collimating lenses and incident on a single region at different incident angles; a sensor configured to detect a positional deviation in diffracted light beams that are diffracted and combined by the first transmission diffraction grating; and a plurality of wavelength selecting elements, each disposed on an optical path between a respective one of the collimating lenses and the first transmission diffraction grating and configured to select a wavelength of a corresponding one of the light beams incident on the first transmission diffraction grating.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2018-104572, filed on May 31, 2018, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to a light source device that emitshigher-power laser light by wavelength beam combining (WBC).

In various fields including laser processing, demand for light sourcedevices that emit high-power laser has been increasing. Examples oflight source devices that emits high-power laser beam include a lightsource device employing wavelength beam combining (hereinafter may alsobe referred to as the “WBC device”). Examples of WBC devices include awavelength-tunable light source device described in JP 2003-324227 A(see FIG. 8 in JP 2003-324227 A). In the wavelength-tunable light sourcedevice described in JP 2003-324227, light beams of different oscillationwavelengths, each emitted from a respective one of a plurality ofsemiconductor lasers, are combined using a diffraction grating.Furthermore, J P 2003-324227 A describes that a portion of the combinedlight beam is branched to be monitored, which allows feedback control ofthe arrangement angle of the combining diffraction grating and theemission angles of light beams from the semiconductor lasers.

SUMMARY

However, using a portion of the combined light beam for monitoring leadsto partial loss of the output light.

An object of the present invention is to provide a light source devicein which a positional deviation in combined light can be detectedwithout affecting the combined light.

A light source device according to one embodiment of the presentinvention includes: a plurality of laser light sources each configuredto emit a light beam; collimating lenses each configured to collimatethe light beam emitted from a corresponding one of the laser lightsources so as to be substantially parallel to an optical axis of thelaser light source; a first transmission diffraction grating configuredto diffract and combine, in an identical diffraction angle direction,the light beams transmitted through corresponding ones of thecollimating lenses and incident on a single region at different incidentangles; a sensor configured to detect a positional deviation indiffracted light beams that are diffracted and combined by the firsttransmission diffraction grating; and wavelength selecting elements eachdisposed on an optical path between a respective one of the collimatinglenses and the first transmission diffraction grating and configured toselect a wavelength of a corresponding one of the light beams incidenton the first transmission diffraction grating. The sensor is configuredto detect the diffracted light beams transmitted through the firsttransmission diffraction grating. The diffracted light beams reflectedby the first transmission diffraction grating is outputted.

A light source device including a sensor in which a positional deviationin combined light can be detected without affecting the combined lightcan be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a light source device according to a firstembodiment of the present invention.

FIG. 2 is a schematic enlarged view of a light source module 100 shownin FIG. 1.

FIG. 3 is a view describing the state of diffraction, reflection, andtransmission of light at a transmission diffraction grating.

FIG. 4 is a schematic view of a linear sensor including a plurality ofphotodiodes.

FIG. 5 is a schematic view of a light source device according to asecond embodiment of the present invention.

FIG. 6 is a view of a sensor and a condenser lens provided in front ofthe sensor.

FIG. 7 is a schematic view of a light source device according to a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to the drawings, certain embodiments of the presentinvention will be described below.

First Embodiment

FIG. 1 is a schematic view of a light source device according to a firstembodiment of the present invention. A light source device 10 accordingto the present embodiment includes a plurality of light source modules100, a first transmission diffraction grating 110, and a sensor 112.Each of the light source modules 100 includes a laser light source 102,a collimating lens 104, a second transmission diffraction grating 106,and a stage 108. In each light source module 100, the laser light source102, the collimating lens 104, and the second transmission diffractiongrating 106 are provided on or in some connection with the same stage108, so that the module can be collectively moved. In this case, thelaser light source 102 is preferably disposed in contact with the stage108, allowing the laser light source 102 to be cooled by cooling thestage 108.

FIG. 1 shows, for the sake of convenience, the x-axis, the y-axis, andthe z-axis being perpendicular to one another. In FIG. 1, broken linesschematically represent light beams. An incident light beam 120 a, anincident light beam 120 b, and an incident light beam 120 c that arerepresented by the broken lines are emitted from their respective laserlight sources 102, pass through their respective collimating lenses 104and second transmission diffraction gratings 106, and are incident onthe first transmission diffraction grating 110. Although each of thebeams is a light beam having an angle of divergence or a width, theoptical axis of each light beam is shown by a broken line in FIG. 1 forthe sake of convenience.

As shown in FIG. 1, in the present embodiment, the incident light beam120 a, the incident light beam 120 b, and the incident light beam 120 care incident on the first transmission diffraction grating 110 atdifferent incident angles. In the present specification, when indicatingan incident light beam that need not be specified, or when indicatingall of the incident light beams, any such incident light beam(s) maysimply be referred to as the “incident light beam(s) 120”. All of theoptical axes of the incident light beams 120 are on the same xz-plane.

The laser light source 102 may be a laser diode (hereinafter referred toalso as the “LD”) having, for example, a peak wavelength in a range of350 nm to 550 nm, and having a predetermined gain spectrum width. Forexample, the laser light source 102 may be an LD including a nitridesemiconductor to emit light with a central wavelength of 410 nm andhaving a gain spectrum width Δλ of 20 nm. In this case, the wavelengthrange of light emitted from the laser light source 102 is from 400 nm to420 nm. More specifically, the laser light source 102 is configured toemit a light beam having a wavelength within a predetermined gainspectrum width (e.g., 400 nm to 420 nm). The wavelength is selected fromwithin the gain spectrum of the light source 102 through externalresonance with the second transmission diffraction grating 106.

When the light emission side of the LD, which is the laser light source102, is the front side, and the side opposite thereto is the rear side,the front side is preferably provided with anti-reflection coating inorder to reduce reflectance to approximately 0%, for example,approximately 0.1% to 2.0%. A mirror on the rear side preferably has areflectance of substantially 100%, for example, a reflectivity in arange of 85% to 99.9%. An LD to emit light in a wavelength range of 350nm to 550 nm is easily deteriorated in the atmosphere and, therefore,the laser light source 102 is preferably hermetically sealed. Forexample, the laser light source 102 may be a CAN-packaged LD. The laserlight source 102 being a CAN-packaged LD further exhibits a coolingeffect, and an effect of blocking static electricity and electromagneticwaves. For the LD to output light having a wavelength in a range of 350nm to 550 nm, a nitride semiconductor can be used.

Each collimating lens 104 collimates the light emitted from thecorresponding laser light source 102 to be substantially parallel to theoptical axis of the laser light source 102. Each collimating lens 104corresponding to a respective one of the laser light sources 102 may bea single lens, or a combination lens being a combination of a pluralityof lenses.

Each second transmission diffraction grating 106 is disposed on theoptical path between the collimating lens 104 and the first transmissiondiffraction grating 110 in a respective light source module 100. Eachsecond transmission diffraction grating 106 diffracts a portion of lightemitted from the laser light source 102 in a respective light sourcemodule 100 to return toward the laser light source 102, causing externalresonance between the laser light source 102 and the second transmissiondiffraction grating 106. More specifically, external resonance occursbetween the rear side of the LD, which is the laser light source 102,and the second transmission diffraction grating 106. That is, each laserlight source 102, a respective collimating lens 104, and a respectivesecond transmission diffraction grating 106 form a single externalcavity. The external cavity may be in the Littrow configuration. TheLittrow configuration refers to a configuration in which the diffractionangle and the incident angle are identical to each other, and thereflected diffracted light is fed back to the light source along theroute identical to that of the incident light.

FIG. 2 is a schematic enlarged view of each light source module 100shown in FIG. 1. The second transmission diffraction grating 106 isdisposed such that a grating groove direction thereof is oriented inparallel to the y-axis shown in FIG. 1. The second transmissiondiffraction grating 106 has a rotation axis 202 parallel to the y-axis.The second transmission diffraction grating 106 can be rotated withrespect to the stage 108 about the rotation axis 202. When the secondtransmission diffraction grating 106 is rotated about the rotation axis202, the arrangement angle of the second transmission diffractiongrating 106 with respect to the laser light source 102 is changed. Thisoperation allows for changing the incident angle of the light emittedfrom the laser light source 102 on the second transmission diffractiongrating. Accordingly, the wavelength of the incident light beam 120transmitted through the second transmission diffraction grating 106 andthe incident light beam 120 on the first transmission diffractiongrating 110 can be selected (changed). That is, each second transmissiondiffraction grating 106 serves as a wavelength selecting element of arespective external cavity.

As shown in FIG. 2, the light source module 100 may be provided with anelement driver 204, so as to control the rotation of the secondtransmission diffraction grating 106. The element driver 204 may be adriving means known in the art such as a stepping motor. For the sake ofconvenience, in the present specification, light emitted from the laserlight source 102 and transmitted through the second transmissiondiffraction grating 106 (the incident light beam 120) may be referred toalso as “a light emitted from the light source module 100” or “a lightemitted from the external cavity”. The incident angle at which theincident light beam 120 is incident on the first transmissiondiffraction grating 110 is determined by the arrangement angle of theexternal cavity that causes the external resonance. More specifically,by selecting the position and angle of each light source module 100 withrespect to the first transmission diffraction grating 110, the incidentangle of the incident light beams 120 can be selected and adjusted.

The first transmission diffraction grating 110 is disposed such that agrating groove direction thereof is oriented in parallel to the y-axisshown in FIG. 1. The incident light beam 120 a, the incident light beam120 b, and the incident light beam 120 c that have been transmittedthrough respective collimating lenses 104 and respective the secondtransmission diffraction gratings 106 of respective corresponding lightsource modules 100 are incident on a single region of the firsttransmission diffraction grating 110, and are diffracted by the firsttransmission diffraction grating 110 at an identical diffraction angleand combined, so that a reflected diffracted light beam 130 is formed.The light source device 10 outputs the reflected diffracted light beam130 in which a plurality of diffracted light beams are combined. Next,with reference to FIG. 3, a description will be given of the state ofdiffraction, reflection, and transmission of light with the firsttransmission diffraction grating 110.

FIG. 3 is a view describing the state of diffraction, reflection, andtransmission of light at the first transmission diffraction grating 110.The dash-dotted line in FIG. 3 represents the normal of the firsttransmission diffraction grating 110. As shown in FIG. 3, when theincident light beam 120 a, the incident light beam 120 b, and theincident light beam 120 c each having been emitted from a respective oneof the light source modules 100 are incident on the first transmissiondiffraction grating 110, the reflected diffracted light beam 130, atransmitted diffracted light beam 140, a reflected light beam 330 a, areflected light beam 330 b, a reflected light beam 330 c, a transmittedlight beam 340 a, a transmitted light beam 340 b, a transmitted lightbeam 340 c and the like are obtained.

The reflected diffracted light beam 130 is first-order diffracted lightreflected by the first transmission diffraction grating 110. Thetransmitted diffracted light beam 140 is first-order diffracted lighttransmitted through the first transmission diffraction grating 110. Thereflected light beam 330 a, the reflected light beam 330 b, and thereflected light beam 330 c are zero-order light reflected by the firsttransmission diffraction grating 110, and correspond to the incidentlight beam 120 a, the incident light beam 120 b, and the incident lightbeam 120 c, respectively. The transmitted light beam 340 a, thetransmitted light beam 340 b, and the transmitted light beam 340 c arezero-order light transmitted through the first transmission diffractiongrating 110, and correspond to the incident light beam 120 a, theincident light beam 120 b, and the incident light beam 120 c,respectively. Second or higher-order diffracted light may also begenerated, but are not shown in FIG. 3 because of having very lowintensity. Furthermore, in a strict sense, the incident light beams 120a, 120 b, and 120 c do not coincide with one another when transmittedthrough the first transmission diffraction grating 110 to formfirst-order diffracted light beams. However, the first-order diffractedlight beams are transmitted through the first transmission diffractiongrating 110 at an identical diffraction angle β, and thus collimated.Therefore, in FIG. 3, the transmitted diffracted light beam 140 isindicated by one optical axis for the sake of simplicity.

In FIG. 3, “αa”, “αb”, and “αc” represent the incident angles of theincident light beam 120 a, the incident light beam 120 b, and theincident light beam 120 c, respectively. “β” represents the diffractionangle of the first-order diffracted light. The optical axes of thereflected diffracted light beam 130, the transmitted diffracted lightbeam 140, the reflected light beam 330 a, the reflected light beam 330b, the reflected light beam 330 c, the transmitted light beam 340 a, thetransmitted light beam 340 b, and the transmitted light beam 340 c arealso on the xz-plane, similarly to the optical axes of the incidentlight beam 120 a, the incident light beam 120 b, and the incident lightbeam 120 c (see FIG. 1).

The sensor 112 is configured to detect the position of the transmitteddiffracted light beam 140 having been transmitted through the firsttransmission diffraction grating 110, thus to detect a positionaldeviation of the reflected diffracted light beam 130. The sensor 112 mayinclude one or more light receiving elements. Examples of lightreceiving elements include a photodiode, a CMOS, a CCD and the like. Inparticular, a photodiode is preferably used for the light receivingelement. Using the photodiode allows for providing the sensor 112 at alow cost. The sensor 112 may be formed of a plurality of light receivingelements or a single light receiving element. The sensor 112 including aplurality of light receiving elements allows for facilitating todetermine the direction of the positional deviation in the diffractedlight. The sensor 112 including a single light receiving element allowsreduction in costs of the light source device.

FIG. 4 is a schematic view of a linear sensor including a plurality ofphotodiodes. As shown in FIG. 4, the sensor 112 may be a linear sensorin which a plurality of light receiving elements are arranged in a line.In the sensor 112 shown in FIG. 4, a plurality of photodiodes 402 arearranged in a line. The sensor 112 is disposed so that the lightreceiving surface of the sensor 112 is perpendicular to the optical axisof the transmitted diffracted light beam 140 while facing thetransmitted diffracted light beam 140, and so that the central axis ofthe direction in which the plurality of photodiodes 402 are arranged(the upper-lower direction in FIG. 4) is on the xz-plane where thetransmitted diffracted light beam 140 exists (see FIG. 1). Thus, asshown in FIG. 4, the sensor 112 can receive the transmitted diffractedlight beam 140.

With each laser light source disposed so that a corresponding incidentlight beam 120 is incident at the correct angle, the sensor 112 candetect the transmitted diffracted light beam 140 at the positioncorresponding to a predetermined diffraction angle. When all of theincident light beams 120 are diffracted by an identical diffractionangle, the diffracted beams are coaxially combined and, therefore, thereflected diffracted light beam 130 with a small beam parameter product(BPP) can be obtained. Meanwhile, when the incident angle of any one ofthe incident light beams 120 is deviated, the transmitted diffractedlight beam 140 shifts in the upper-lower direction in FIG. 4 withrespect to the sensor 112, or the shape of the beam is expanded in theupper-lower direction in FIG. 4. Thus, the sensor 112 detects thepositional deviation in the transmitted diffracted light beam 140. Whenthe incident angle of the incident light beam 120 is deviated, theposition of the reflected diffracted light beam 130 is also deviated,similarly to the transmitted diffracted light beam 140. Therefore,detecting the positional deviation in the transmitted diffracted lightbeam 140 allows for also detecting the positional deviation in thereflected diffracted light beam 130.

When the sensor 112 detects the positional deviation in the lightdiffracted by the first transmission diffraction grating 110, adjustingthe angle of the second transmission diffraction grating 106 to changethe wavelength of light incident on the first transmission diffractiongrating 110 allows for correcting the positional deviation of thediffracted light of the first transmission diffraction grating 110. Thiswill be described below with a specific example.

When the incident angle of the incident light beam 120 incident on thefirst transmission diffraction grating 110 is α and the diffractionangle of the light diffracted by the first transmission diffractiongrating 110 is β, the relationship of Equation 1 is satisfied:

sin α+sin β=N·m·λ  Equation 1

where N is the number of grooves per a length of 1 mm in the firsttransmission diffraction grating 110, which is a combining diffractiongrating, m is the order of 1 diffraction, and λ is the wavelength oflight.

For example, the first order diffraction is discussed, assuming thateach laser light source 102 emits a laser beam having a centralwavelength of 410 nm and has a wavelength range of 400 nm to 420 nm, andthe number of grooves per a length of 1 mm in the first transmissiondiffraction grating 110 is 2222. In this case, laser beams with thewavelength λ and at the incident angle α in combinations shown in Table1 are diffracted at the identical diffraction angle β and are combinedto produce a combined beam.

TABLE 1 diffraction wavelength λ (nm) incident angle α (degrees) angle β(degrees) 402.93 43.74 11.77 405.30 44.16 11.77 407.66 44.58 11.77410.00 45.00 11.77 412.32 45.12 11.77 414.63 45.84 11.77 416.92 46.2611.77

For example, the angle of the second transmission diffraction grating106 of each light source module 100 shown in FIG. 1 is adjusted so thatthe incident light beam 120 a, the incident light beam 120 b, and theincident light beam 120 c have wavelengths of 414.63 nm, 410.00 nm, and405.30 nm, respectively. Furthermore, the position of each light sourcemodule 100 is adjusted so that the incident light beam 120 a (see FIG.3) has an incident angle αa of 45.84 degrees, the incident light beam120 b has an incident angle αb of 45.00 degrees, and the incident lightbeam 120 c has an incident angle αc of 44.16 degrees. Then, all of thelight beams emitted from the light source modules 100 are diffracted atan identical diffraction angle β of 11.77 degrees by the firsttransmission diffraction grating 110, so that the high-power reflecteddiffracted light beam 130 is formed. At this time, the transmitteddiffracted light beam 140 is also formed. The sensor 112 can detect theposition of the transmitted diffracted light beam 140. All of theincident light beams 120 are diffracted by an identical diffractionangle and are combined coaxially, so that the light source device 10 canoutput a high-quality light beam.

While the above description illustrates that the incident light beam 120a having a wavelength of 414.63 nm is incident at the predeterminedincident angle of 45.84 degrees, a case will now be considered whereincident light with a wavelength of 414.63 nm from actual light sourcemodules 100 a is incident at an incident angle of 46.26 degrees. In thiscase, the diffraction angle β of the first-order diffracted light of theincident light beam 120 a calculated using Equation 1 is 11.47 degrees,which is different from the predetermined value of 11.77 degrees. Withsuch a diffraction angle β, the diffracted light combined by the firsttransmission diffraction grating 110 (the reflected diffracted lightbeam 130 and the transmitted diffracted light beam 140) fails to becoaxial and the BPP of the combined beam is increased, resulting in poorquality. As described above, it is not easy to precisely adjust thelight source modules 100 in trying to adjust the incident angle α to bea proper angle while irradiating one portion of the first transmissiondiffraction grating 110, which is the combining diffraction grating,with a laser light beam. Thus, it is considered difficult to correctsuch a deviation in the incident angle by adjusting the angle of thelight source modules 100.

On the other hand, in the light source device 10 according to thepresent embodiment, each light source module 100 includes the secondtransmission diffraction grating 106 serving as a wavelength selectingelement. When the sensor 112 detects a deviation in the diffractedlight, the angle of the second transmission diffraction grating 106 canbe adjusted for each light source module 100. In the light source device10 according to the present embodiment, changing the wavelength of theincident light beam 120 a, which is incident on the first transmissiondiffraction grating 110 at an incident angle of 46.26 degrees, to 416.92nm enables an adjustment of the diffraction angle of the diffractedlight of the incident light beam 120 a from 11.47 degrees to 11.77degrees. Thus, tolerance of positional deviations in the light sourcemodule 100, which is difficult to adjust in position, can be increased.

Furthermore, the light source device 10 according to the presentembodiment does not require devices such as a beam analyzer or aspectrum analyzer, which have high-performance and are expensive, sothat the light source device 10 according to the present embodiment canhave a simple structure, and increase in cost can be reduced.Furthermore, the sensor 112 is generally provided in the light sourcedevice 10. Therefore, when the incident angle is deviated due to somefactor after shipment of the light source device 10, the sensor 112 canimmediately detect a positional deviation in the diffracted light.

In view of its function, the first transmission diffraction grating 110preferably allows to pass a smaller amount of light as a transmittedlight beam and reflects a greater amount of light as a reflected lightbeam. This is different from the second transmission diffraction grating106, which is also a transmission diffraction grating. The firsttransmission diffraction grating 110 has a transmittance with respect tothe zero-order light lower than a transmittance of the secondtransmission diffraction grating 106 with respect to the zero-orderlight. For example, the ratio of the reflected diffracted light beam 130(i.e., the reflected first-order diffracted light) outputted from thefirst transmission diffraction grating 110 (i.e., the reflectance of thefirst transmission diffraction grating 110 with respect to thefirst-order diffracted light) may be in a range of 70% to 99%,preferably in a range of 85% to 99%. The ratio of the transmitteddiffracted light beam 140 (i.e., the transmitted first-order diffractedlight), that is, the transmittance with respect to the first-orderdiffracted light, may be in a range of 0.1% to 10%, preferably in arange of 0.1% to 5%. The ratio of the transmitted zero-order light(i.e., the transmittance with respect to the zero-order light) may be ina range of 0.1% to 10%, preferably in a range of 0.1% to 5%. Forexample, for the first transmission diffraction grating 110, atransmission diffraction grating having a reflectance of 97% of thefirst-order diffracted light, a transmittance of 1% of the first-orderdiffracted light, and a transmittance of 1% of the zero-order light ofmay be used.

The second transmission diffraction grating 106 preferably allows topass a greater amount of light as a transmitted light beam and reflectsa smaller amount of light as a reflected light beam. The secondtransmission diffraction grating 106 has a transmittance with respect tothe zero-order light higher than the transmittance of the firsttransmission diffraction grating 110 with respect to the zero-orderlight. For example, the ratio of the zero-order light transmittedthrough the second transmission diffraction grating 106 (i.e.,transmittance of the second transmission diffraction grating 106 withrespect to the zero-order light) may be in a range of 60% to 90%,preferably in a range of 73% to 83%.

The ratio of the reflected first-order diffracted light (i.e., thereflectance with respect to the first-order diffracted light) may be ina range of 10% to 30%, preferably in a range of 15% to 25%. The ratio ofthe transmitted first-order diffracted light (the transmittance withrespect to the first-order diffracted light) may be in a range of 0.1%to 5%, preferably in a range of 0.1% to 2%. For example, for the secondtransmission diffraction grating 106, a transmission diffraction gratinghaving a transmittance with respect to the zero-order light of 78%, areflectance with respect to the first-order diffracted light of 20%, atransmittance with respect to the first-order diffracted light of 1% maybe used.

With the light source device according to the present embodiment havinga structure as described above, when the sensor receives a transmitteddiffracted light beam, the degree of combining of output light can beevaluated using the positional deviation in the transmitted diffractedlight beam that does not contribute to output. This allows for reducingloss of the output light.

Furthermore, branching of the output light is not necessary whendetecting a positional deviation, so that an optical element necessaryfor the branching is not disposed. This allows for reducingdeterioration in beam quality.

Furthermore, employing the transmission diffraction grating for thecombining diffraction grating allows for reducing light absorption bythe diffraction grating, so that deterioration of the diffractiongrating can be reduced. When using a reflective diffraction gratingprovided with a metal film at a light incident surface, the reflectivediffraction grating absorbs light, which may lead to deterioration ofthe reflective diffraction grating.

Second Embodiment

FIG. 5 is a schematic view of a light source device according to asecond embodiment of the present invention. A light source device 50according to the present embodiment is a modification of the lightsource device 10 according to the first embodiment. In the presentembodiment, components, members, parts, devices, and/or elements havingthe same functions as those in the first embodiment are denoted by thesame reference characters as those in the first embodiment, and thedescription thereof may be omitted.

The light source device 50 is different from the light source device 10mainly in that the sensor 112 is disposed adjacent to the laser lightsources 102, and the transmitted diffracted light beam 140 transmittedthrough the first transmission diffraction grating 110 is guided to thesensor 112 by a mirror 502 and a mirror 504.

As shown in FIG. 5, the light source modules 100 are preferably providedwith a light source cover 512. With the sensor 112 being disposedadjacent to the laser light sources 102, effects as described below canbe further obtained. Using a portion of the light source cover 512, asensor cover 514 can be easily provided. When the sensor 112 is providedwith the sensor cover 514, noise of light in the surrounding can beblocked, so that accuracy in detection of the sensor 112 can beimproved. While the sensor 112 disposed near the first transmissiondiffraction grating 110 is easily influenced by stray light attributedto the zero-order light transmitted through the first transmissiondiffraction grating 110, when the sensor 112 is disposed adjacent to thelaser light sources 102, the sensor 112 can be prevented from beinginfluenced by such stray light. Furthermore, the distance between thefirst transmission diffraction grating 110 and the sensor 112 can beincreased, allowing the deviation in the diffracted light to benoticeable, so that accuracy in detection can be increased.

FIG. 6 is a view of the sensor 112 and a condenser lens provided infront of the sensor 112. As shown in FIG. 6, a condenser lens 600 may befurther disposed on the optical path of light becoming incident on thesensor 112. In this case, the sensor 112 is disposed at the rear focalplane of the condenser lens 600. The optical axis of the condenser lens600 is aligned with a desired optical axis of the transmitted diffractedlight beam 140. In FIG. 6, in order to describe the effect of thecondenser lens 600, the transmitted diffracted light beam 140 is shownas a beam that has a certain width. As represented by broken lines, thetransmitted diffracted light beam 140 includes transmitted diffractedlight beams 140 a, 140 b, 140 c, 140 d, and 140 e. The transmitteddiffracted light beam components 140 a, 140 b, and 140 c are collimatedlight components which are parallel to a desired optical axis of thetransmitted diffracted light beam 140, and the transmitted diffractedlight beam components 140 d and 140 e are components with deviateddiffraction angles due to deviations in the incident angle of theincident light beam 120.

As shown in FIG. 6, while the transmitted diffracted light beamcomponents 140 a, 140 b, and 140 c that are parallel to a desiredoptical axis of the transmitted diffracted light beam 140 are condensedat one point by the condenser lens 600, the transmitted diffracted lightbeam components 140 d and 140 e that are not parallel to a desiredoptical axis of the transmitted diffracted light beam 140 cannot becondensed to the same point. That is, with the condenser lens 600,deviated diffracted light components and diffracted light components notbeing deviated can be separated from each other among the transmitteddiffracted light beam 140, so that, accuracy in detection of the sensor112 can be further improved.

Third Embodiment

FIG. 7 is a schematic view of a light source device according to a thirdembodiment of the present invention. A light source device 80 accordingto the present embodiment is a modification of the light source device10 according to the first embodiment. In the present embodiment,components, members, parts, devices, and/or elements having the samefunctions as those in the first embodiment are denoted by the samereference characters as those in the first embodiment, and thedescription thereof may be omitted.

The light source device 80 is different from the light source device 10mainly in configurations described below. Each laser light source 102 isa laser diode forming a laser diode bar 802. In the laser diode bar 802a plurality of (e.g., five in the example in FIG. 7) laser diodes arearranged in an array in the x-axis direction on the same substrate. InFIG. 7, the laser light sources 102, which are laser diodes, areindicated by broken lines representing waveguides corresponding to thelaser light sources 102. A deflection condenser lens 810 is disposed onthe optical path between the second transmission diffraction gratings106 and the first transmission diffraction grating 110.

The incident light beam 120 a, the incident light beam 120 b, theincident light beam 120 c, the incident light beam 120 d, and theincident light beam 120 e transmitted through the second transmissiondiffraction grating 106 and emitted from each external cavity propagateparallel to one another to the deflection condenser lens 810 in thez-axis direction shown in FIG. 7. The incident angle at which eachincident light beam 120 is incident on the first transmissiondiffraction grating 110 is determined by the deflection condenser lens810. That is, the incident light beam 120 emitted from each externalcavity is incident on the first transmission diffraction grating 110 ata proper incident angle determined by the deflection condenser lens 810.The incident light beams 120 are diffracted by the first transmissiondiffraction grating 110 at the identical diffraction angle and combined,to form the reflected diffracted light beam 130 and the transmitteddiffracted light beam 140.

In the present embodiment, a lens array in which a plurality ofcollimating lenses, each of which corresponding to a corresponding oneof the laser diodes of the laser diode bar 802, are integrated may beused for the collimating lens 104. The laser diode bar 802 including aplurality of laser light sources 102 is preferably hermetically sealed.For example, the entirety of the laser diode bar 802 may be hermeticallysealed.

As in the light source device 10, the sensor 112 detects the position ofthe transmitted diffracted light beam 140. Accordingly, as in the lightsource device 10, the light source device 80 according to the presentembodiment can detect positional deviation (i.e., deviation indiffraction angle) of the diffracted light using the sensor 112.Further, by adjusting the angle of the second transmission diffractiongrating 106, the positional deviation in the diffracted light can beeasily corrected.

While certain embodiments of the present invention has been describedabove, the technical scope of the present invention is not limited tothe description of the embodiments illustrated above. It is to beunderstood that various other embodiments and variants within the scopeand spirit of the invention may occur to those skilled in the art, andsuch other embodiments and variants are intended to be covered by thefollowing claims. For example, the embodiments described above isdescribed in detail for ease of understanding of the present invention,and the present invention is not limited to those including all of thestructures described above.

Some of the configurations in the described embodiments may be replacedby other configurations, or may be eliminated. Furthermore, some of theconfigurations in some embodiments may be added to configurations inother embodiments. For example, in the first and third embodiments, asin the second embodiment, the condenser lens 600 may be further disposedon the optical path of light to be incident on the sensor 112.

What is claimed is:
 1. A light source device comprising: a plurality oflaser light sources, each configured to emit a light beam; a pluralityof collimating lenses, each configured to collimate the light beamemitted from a corresponding one of the laser light sources so as to besubstantially parallel to an optical axis of the laser light source; afirst transmission diffraction grating configured to diffract andcombine, in an identical diffraction angle direction, the light beamstransmitted through the collimating lenses and incident on a singleregion at different incident angles; a sensor configured to detect apositional deviation in diffracted light beams that are diffracted andcombined by the first transmission diffraction grating; and a pluralityof wavelength selecting elements, each disposed on an optical pathbetween a respective one of the collimating lenses and the firsttransmission diffraction grating and configured to select a wavelengthof a corresponding one of the light beams incident on the firsttransmission diffraction grating, wherein the sensor is configured todetect diffracted light beams transmitted through the first transmissiondiffraction grating, and wherein the light source device is configuredto output diffracted light beams reflected by the first transmissiondiffraction grating.
 2. The light source device of claim 1, wherein thesensor and the wavelength selecting elements are configured such that,when the sensor detects a positional deviation in one or more of thediffracted light beams diffracted by the first transmission diffractiongrating, an angle of a corresponding one or more of the wavelengthselecting elements is adjusted to change a wavelength of the light beamsto be incident on the first transmission diffraction grating, correctingthe positional deviation in the one or more of the diffracted lightbeams diffracted by the first transmission diffraction grating.
 3. Thelight source device of claim 2, further comprising: a mirror, whereinthe sensor is disposed adjacent to the laser light sources, and whereinthe mirror is configured to guide the diffracted light transmittedthrough the first transmission diffraction grating to the sensor.
 4. Thelight source device of claim 1, wherein each of the wavelength selectingelements is a second transmission diffraction grating, wherein atransmittance of the second transmission diffraction grating withrespect to zero-order light is higher than a transmittance of the firsttransmission diffraction grating with respect to zero-order light, andwherein the light source device further comprises a plurality of elementdrivers, each configured to change an arrangement angle of a respectiveone of the second transmission diffraction gratings with respect to acorresponding one of the laser light sources, to change the wavelengthof the light beam to be incident on the first transmission diffractiongrating.
 5. The light source device of claim 1, wherein the sensorcomprises a plurality of light receiving elements.
 6. The light sourcedevice of claim 5, wherein the sensor is a linear sensor in which thelight receiving elements are arranged in an array.
 7. The light sourcedevice of claim 1, wherein the sensor is a single light receivingelement.
 8. The light source device of claim 1, further comprising: acondenser lens disposed on an optical path of light to be incident onthe sensor, wherein the sensor is disposed on a rear focal plane of thecondenser lens.
 9. The light source device of claim 1, wherein each ofthe laser light sources comprises a nitride semiconductor, and whereinthe laser light sources are hermetically sealed.
 10. The light sourcedevice of claim 1, wherein the laser light sources are laser diodesforming a laser diode bar, and wherein an incident angle of each of thelight beams incident on the first transmission diffraction grating isdefined by a deflection condenser lens disposed on an optical pathbetween the wavelength selecting element and the first transmissiondiffraction grating.